Stronger intensity of 10–30-day intraseasonal waves over the North Pacific in early summer than late summer

Atmospheric teleconnections or wave trains, such as the well-known PNA (Pacific–North America) pattern, are of great importance because they can link weather and climate between regions separated by vast distances. Studying these teleconnections or wave trains can help us better understand the climatic links between different regions, and also has implications for climate prediction.

In 2021, Lei Du and Prof. Riyu Lu, from the Institute of Atmospheric Physics, Chinese Academy of Sciences, identified intraseasonal wave trains over the North Pacific. The wave trains are zonally oriented along the upper-tropospheric westerly jet, with their dominant period being 10–30 days. They mainly obtain energy from the basic flow through baroclinic energy conversion to develop and maintain themselves. Climatologically, the westerly jet core jumps rapidly from the North Pacific to Eurasia in July, indicating that the westerly jet is weakened in late summer compared with early summer.

In a newly published paper in Atmospheric and Oceanic Science Letters, Du and Lu have verified that the westerlies over the upper North Pacific in early summer (1 June to 7 July) are significantly stronger compared with late summer (8 July to 31 August), and indicated that the wave trains are significantly stronger in the early summer than in the late summer. The major reason is that the wave trains can gain more energy from stronger westerlies through baroclinic energy conversion in the early summer. 

“The present results imply that the weather and climate links between East Asia and North America may also change subseasonally during summer, which requires further investigation in the future,” says Prof. Lu.